Generally, semiconductor light emitting diode (LED) receives attention from various fields as an environment friendly light source. Recently, as applications of LEDs are expanding to various fields such as interior and exterior illuminations, automobile headlights, and back-light units (BLU) of display devices, there are needs for high optical efficiency and excellent heat radiation characteristics. For high efficiency LEDs, materials or structures of the LEDs should be improved primarily, however there is a need for improvement in the structures of the LED packages and the materials used therein.
In such high efficiency LEDs, high temperature heat is produced, therefore this heat must be radiated effectively otherwise temperature rising on the LEDs causes ageing of the characteristics thereby shortening the lifetime. In high efficiency LED packages, efforts on effective radiation of the heat produced by the LEDs are making progress.
Hereinafter, any kind of device that emits light including LED will be referred to as ‘optical device,’ and any product including more than two optical devices will be referred to as ‘optical device.’
Meanwhile, UV light emitting diodes or short-wavelength visible light emitting laser diodes or the like are manufactured as a can package-type wherein inert gas, for example, nitrogen gas and the like is sealed; FIG. 1 is a cross-sectional view of an optical device according to an example of a can package-type of the prior art, and it is disclosed in Korea patent No. 1021210.
As shown in FIG. 1, in an optical device 1 inert gas is sealed in an airtight space configured by a metal stem 8 and a can cap 9, and the semiconductor light emitting element 4 is provided in the airtight space and is fixed to the metal stem 8 through a substrate 2.
A ceramic block 13 is fitted into an opening in the metal stem 8 wherein a pair of electrode terminals 10a and 10b are extended out of the airtight space through the ceramic block 13, and the electrode terminals 10a and 10b and the semiconductor light emitting element 4 are electrically coupled with each other by wires.
An opening 11 is formed on the upper face center of the can cap 9, and the opening 11 is sealed with a transparent plate 12 sealing inside of the can cap 9. A phosphor layer 7 is formed in the opening 11.
Peripheral portions of the metal stem 8 and the can cap are bonded by welding or the like, thereby forming an airtight space.
It is preferred that the metal stem 8 and the can cap 9 are made of the same material, for example, single metal material such as aluminum or cobalt, however, alloy such as cobalt or copper-tungsten may also be used. In the airtight space, the metal stem 8 supports the semiconductor light emitting element 4 and radiates heat generated by the semiconductor light emitting element 4 out of the airtight space. Thus, it is preferred that the metal stem 8 is made of a material having high thermal conductivity.
The inert gas sealed into the airtight space is, for example, at least one inert gas of nitrogen, helium, or argon, thereby preventing the semiconductor light emitting element 4 from being deteriorated.
The ceramic block 13 is a non-conductive member such as, for example, alumna or aluminum nitride, which is fitted and fixed to an opening formed in the metal stem 8, thereby electrically insulating the electrode terminals 10a and 10b from the metal stem 8. The semiconductor light emitting element 4 is fixed to the substrate 2 by solder or the like, and the substrate 2 is fixed to the metal stem 8 by solder or the like.
The electrode terminals 10a and 10b are comprised of conductive materials, for example, they may be formed by a punching process of a metal plate. The transparent plate 12 is a sheet-shaped member made of a transparent material such as glass and resin, and may be a convex shape or a concave shape to provide a lens effect.
According to the foregoing can package-type optical device of the prior art, since the metal stem merely supports the semiconductor light emitting element, for applying power to the semiconductor light emitting element, two electrical terminals penetrating said airtight space and a ceramic block 13 and the like are required, thereby resulting problems of complicated structure and difficult manufacturing process. Besides, there is a problem of degradation in reflection efficiency and heat dissipation capability.